[Old Boy]

I do not recall any of my previous cars letting water seep inside doors to such an extent as it happens with my 19 M550. This is my first BMW ever, and perhaps that is the way all of their vehicles behave ?

It doesn't take much rain or carwash (no excessive waterjets directed at the windows) for some water to accumulate inside all four doors.....I see water on the windows when lowered-raised. In warm weather it is all gone within a day or less if the car is in direct sunlight.

I understand that there are moisture weep holes in the door bottoms, however, I wonder what might happen to window operation in our frigid winters. Additionally, there is always a concern about long term rusting.

What is your experience with this issue ?

[Dephead2004]

Quite normal. The window seals are never a tight seal and so there is a membrane in the door card to prevent the water from entering the vehicle itself.
Modern standards of rust proofing are very high and in case of error in application you have a 10 year rust through warranty. Electrics on the damp side are also waterproofed especially at the connectors.

In this case it's true: they're all like it, Sir.